The technical field of this invention is the deployment of an occupant restraint in a motor vehicle during a vehicle crash event.
The control of occupant restraints for motor vehicles is becoming more complex with development of multiple stage restraints, wherein the initial detection of a crash signals a first stage deployment and a second stage deployment is signaled only in a more severe crash. Thus, a requirement for such systems is a crash severity measurement system for second stage deployment that is accurate, reliable and as economical as possible. The problems include the complexity of the task, the difficulty of accurately and reliably distinguishing crash from non-crash events with the available sensors, and the memory load placed on microcomputers used in the control, since the volume of code required appears to be increasing faster than the cost of CPU and memory capacity is falling.
The method and apparatus of this invention is a dual stage occupant restraint deployment control that is accurate, reliable and cost effective. It is particularly directed toward such a system for use in a passenger compartment located acceleration sensor and including a dual stage restraint system for frontal crashes, although it is not necessarily limited to such systems.
The method and apparatus of this invention provides a signal for first stage restraint deployment if, during a sensed possible crash event, a velocity value derived from a sensed acceleration and one or more immunity measures meet predetermined criteria. A second stage restraint deployment signal is provided if a crash severity measure derived from the time rate of change of the sensed acceleration meets predetermined criteria and the first stage activation signal has been generated. The method and apparatus ensure that the immunity criteria are met for both first and second stage deployment without repeated testing if the crash severity measure is vulnerable to non-crash accelerations produced by xe2x80x9cmisusexe2x80x9d events and rough road driving. The crash severity measure may be the time rate of change of the acceleration itself, an oscillation value derived this time rate of change of the acceleration with a velocity value requirement in the predetermined criteria, or a veloscillation value derived from the oscillation value and the velocity value.